# Homework Help: Magnetic Field and electron beam

1. Oct 4, 2008

### strawberrysk8

1. The problem statement, all variables and given/known data

The original direction of the electron beam as it enters the magnetic field is along the earth’s magnetic field. If the magnitude of the earth’s magnetic field is 0.1 mT and the magnetic field due to the Helmholtz coils is 1.0 mT (perpendicular to the electron beam), the resulting path of the electron can be best described as:

a) A helical path with the axis of the helix roughly along the earth’s magnetic field.

b) A helical path with the axis of the helix roughly along the Helmholtz coils magnetic field.

c) A straight line

2. Relevant equations

3. The attempt at a solution

which is it? I have no idea!

2. Oct 4, 2008

### Hootenanny

Staff Emeritus
We will help you, but don't give out answers here. "I have no idea" isn't an attempted solution. Work though each option logically and post your thoughts on why it could [not] be each one and we'll take it from there.

3. Oct 4, 2008

### strawberrysk8

I am leaning towards c) a straight line.

I feel like the only way for an electron to move in a helical path is for the two magnetic fields to be diagonally intersecting.

4. Oct 4, 2008

### Gear300

Take into consideration the net magnetic field vectors...once you do so...take into consideration of what happens when the magnetic fields are not perpendicular to the velocity.

Last edited: Oct 4, 2008
5. Oct 4, 2008

### strawberrysk8

ok... then maybe b) since the strength of the helmholtz coil's magnetic field is larger than the strength of earth's magnetic field. so the electron will follow a circular path, but along mostly the helmholtz coil's magnetic field